The present invention relates to a well logging method and apparatus and more particularly to a method and apparatus which enables efficient and rapid logging of a well.
In oil and gas exploration it is extremely important to produce logs of each well in order that the oil/gas producer can assess the potential output of the well and know where to perforate.
Whilst such well logging is beneficial, it can be extremely expensive due to several factors, one of which is the time taken to produce the log.
When logging a well the drilling rig is required to stand idle from its drilling operation. The hire cost of such offshore rigs is very expensive and time taken to acquire data from conventional well logging of horizontal holes can be several days.
It is an object of the present invention to provide a well logging method and apparatus which enables a well to be logged in a much shorter time period than is possible with conventional methods.
It is a further object of the present invention to provide a well logging method and apparatus which is applicable to small diameter short length logging tools.
The present invention provides a method of well logging comprising the steps of:
a) inserting a battery powered memory logging device into a well borehole at a head end of said well, said well borehole containing a drill pipe;
b) forcing said logging device to a position adjacent to the far end of said drill pipe, opposite to said head end, by means of pump pressure applied to said logging device, said pump pressure being applied along said drill pipe from said head end;
c) maintaining pump pressure on said logging device;
d) pulling back on said drill pipe over a defined length whilst maintaining said pump pressure to expose at least a portion of the logging tool containing logging sensors into the open borehole at the end of the drill pipe;
e) pulling said drill pipe through said borehole towards said head end;
f) maintaining the pump pressure to maintain the position of the logging portion of the logging device protruding from the end of the drill pipe; and
g) logging the characteristics of the well with said logging device as said drill pipe is pulled through said well borehole.
Preferably the method further comprises the steps of:
h) once logging of the borehole over a required distance has been completed, reversing the pump pressure in said drill pipe such that pump pressure is applied to the end of said logging device furthest from said well head;
i) forcing said logging tool along said borehole towards said well head; and
j) catching said logging tool at a position adjacent said well head.
Preferably said method further comprises k) removing said logging device from said well head and down-loading said recorded logging data.
The invention also provides a well logging tool for use with the above method, said well logging tool comprising a first portion comprising well logging sensors and a second portion comprising a retention portion, said retention portion being provided with collar means for retaining said logging device within said drill pipe.
Preferably said retention portion of said well logging tool includes means for passage of fluid through said tool.
Conveniently the well logging tool is constituted as an open hole battery memory tool.